Here is the reason for all the dead fish in Koocanusa this past weekend.
Fishing - Region 1
A strong and fast moving storm front last Sunday night appears to have triggered a kokanee salmon
die-off in Lake Koocanusa August 26 and 27. Fisheries biologist Mike Hensler estimates there were
at least 10,000 dead juvenile kokanee measuring 8”-10” long scattered from Big Creek to the
Canadian border.
This kill is similar to a die-off in 2005 and several others in the 1990s and earlier. The mortality
appears to be triggered by a period of calm, hot weather that lets the reservoir stratify and allows
algae to bloom. The storm front, accompanying winds and drop in atmospheric pressure allows the
algae to mix with deeper layers. The kokanee ingest the algae, which includes some blue-green
algae which is toxic to the fish, as they are feeding. They become disoriented, come to the surface,
their air bladders expand and they are unable to dive back to depth so the warm surface water kills
them.
The algae is not abundant enough to affect humans and has now been dispersed by continuing
winds. Likewise, the die-off only lasted a few days and only affected a small portion of what would be
next year’s adult salmon. There are no health concerns with eating a fish healthy enough to hit a
lure.
Contact : Mike Hensler, Libby Field Satation, 406-293-4161, ext. 204
Attached: Detailed explanation by Fisheries Biologist Mike Hensler